Several bacterial polysaccharides contain a terminal lipid moiety which causes the polysaccharide to aggregate. It has been proposed that the lipid tail of Group C polysaccharide (GCPS) from N. meningitidis might anchor the polysaccharide to the outer membrane. Our studies have found that incubation of native GCPS with isolated outer membrane vesicles results in about 15% association of the polysaccharide with the outer membrane. Removal of the lipid terminal from the native GCPS with phospholipase A2 (PL) treatment eliminates this association. It also makes the polysaccharide unsuitable for use as an antigen on a solid surface in an ELISA to measure antibodies against the polysaccharide. Antibody units measured in the sera of carriers and vaccinees of group C N. meningitidis using PL treated GCPS as an antigen were 10% of the values obtained with native GCPS. However, in solution, GCPS without the terminal lipid bound antibody as effectively as native GCPS when used in a competitive inhibition assay. Hence, removal of the lipid tail results in no discernible alteration in the antigenic epitopes.